Screw-propeller



(ModeL) v 2-811eets -Sheet 1.

A. W. CASE; SCREW PROPELLERL Patented Feb. 4,1896.

ANDREW B.GRAMAM. PHUTOUTNQWABHINETOM 0.6

. UNITED STATES PATENT Crrrcn.

ALFREDWVELLS CASE, OF HIGHLAND PARK, CONNECTICUT.

SCREW-PROPELLER.

SPECIFICATION forming part of Letters Patent No. 553,953, dated February4, 1896.

Application filed September 21, 1895. Serial No. 563,279. (ModeL) I ToaZZ whom it may concern:

Be it known that I, ALFRED WELLS CASE, a citizen of the United States,and aresident of Highland Park, in the county of Hartford and State ofConnecticut, have invented certain new and useful Improvements in Screw-Propellers, of which the following is a full, clear, and exactdescription, whereby any one skilled in the art can make and use thesame.

The object of my invention is to provide a screw-propeller of suchconstruction as to secure a more efficient thrust upon the water in therotation of the screw, to secure a smoothlyrunning screw which shalltend to reduce vibration, and also to provide one in which the outwardand rearward thrust of the blades can be obtained without requiring theblade to be inclined so far forward as to encounter the stern-post,bracket, or web of the ship or boat to which the screw is fitted.

To this end my invention consists in the details of the several partsmaking up the screw-propeller as a whole, and including the disposition,location,and arrangement of each blade, as more particularly hereinafterdescribed and pointed out in the claim.

Referring to the drawings,Figure 1 is a front view in elevation of afour-bladed screw constructed in accordance with my invention. Fig. 2 isa detail side View of the screw of the improved form. Fig. 3 is aperspective view of my improved screw-propeller as applied to a vessel.

In the accompanying drawings, the letter a denotes a screw-propellercomprising a hub b and a number of blades 0 projecting therefrom, eachblade having its working surface located in such position with referenceto the hub b and the axis of the screw that a line 1, common to theworking surface of the blade at its center, if prolonged shall not passthrough the axis of the hub; and as a result of this substantially thewhole of the working surface of the blade will be located at an anglewith any radius 3, which extends from the axis 2 of the hub and passesthrough the root of the blade. Each blade preferably has its workingsurface formed by a straight generatrix and conforming to any desiredpitch.

The working surface of the blade at the leading edge 0', and for adistance backward therefrom extending beyond the center line,

rakes backward from a radial line 3 drawn through a point, as 0 at theroot of the blade; and this angular location of the blade, as described,so places it with reference to the hub as to enable an outward andrearward thrust upon the surrounding mass of water to be obtaiued. Theblade is also forwardly inclined, although the leading edge 0 does notnecessarily overhang the front end of the hub. This feature of forwardinclination is illustrated by the location of the center line, 4, inFig. 2 of the drawings, which extends from the center of the workingsurface at the root of the blade outward through the center of thesurface to the tip of the blade. The angle which this line 4 makes withthe axis 2 is the angle of forward inclination.

lVhen so constructed, the wheel will easily fit within a narrow space atthe stern of a boat with no danger of the leading edge 0 of the bladestriking the stern-post, bracket or web, the blade in a prior wheel ofthis class, which has an extreme inclination forward, having in someinstances been a detriment to the ready fitting of a wheel whichembodies the features of improvement residing in that location of theblade which produces a backward and outward thrust when an attempt hasbeen made to fit such a prior wheel to a boat in replacing an old typeof propellerwheel.

The main feature of my invention resides in the peculiar location of theworking surface of the blade on a line at an angle with a radius of thewheel, as herein described, the working surface of the screw beingpreferably formed, as stated, by a straight generatrix and conforming toany desired pitch.

The working surface of my improved blade as I have constructed wheels isformed on an expanding pitch substantially straight from root to tip andwith the backward rake and forward inclination at the ratio of twoinches to each foot in length of the blade. The back of the blade iscurved or made full to an extent sufficient to give proper strength bythickening the center when the leading and following edges are workedfine to produce the proper impact and avoid drag.

My invention is not limited to a wheel in which the blade shall have itsworking surface formed bya straight generatrix, nor is an expandingpitch and the exact ratio of compound inclination important, thesefeatures, as stated, being variable at will and depending upon the sizeof the wheel and work to be performed.

Each blade is offset at the root, so that the generat-rix does notextend through the axis of the hub when the center line of the blade isprolonged inward, and this particular location of the working surfacewith reference to a radial line and including the compound slope-thatis, the backward rake and forward inclination referred to--distinguishthe improvement from prior blades.

In the accompanying drawings a propeller has been shown with fourblades; but this particular number of the blades and the preciseproportions of each blade are not essential features of the improvement,which resides, as stated, in the peculiar construction and location ofeach blade as a whole, whereby as a result of the compound inclinationthe advantages of the outward and rearward thrust and the arrangement ofthe blade within a limited space lengthwise of the propeller areobtained.

From tests which have been made with a with the within invention it hasbeen found that there is an almost entire absence of vibration, a gainin speed over wheels of other types, and a reduction of the amount ofcoal consumed, and, further, that the blade constructed as described isparticularly effective in stopping a boat promptly and in backing. Thetests have shown that a vessel under a certain headway could be broughtto a complete stop and backed quicker in a less distance when going at agiven rate of speed than with screws of the prior art.

I claim as my invention- A screw-propeller having a hub and a series ofblades arranged about and projecting from it, each blade inclinedforward in the direction of forward motion of the vessel as described,and also having its working surface at its center line oifset andlocated in a plane raking backward at an angle from a radius passingthrough the root of the blade and in the plane of rotation of the screw,whereby a rearward and outward thrust upon the water is obtained in aforward rotary movement of the wheel, all substantially as described.

ALFRED \VELLS CASE.

Witnesses:

mus. L. BURDETT, ARTHUR B. JENKINS.

